1. Field of the Invention
This invention relates to a cast cold tool made of a casting obtained through a founding process and, more particularly to the cast cold tool used for a cold press die, a cold die, a cold header die, an upsetting die and so on, for example, and a method for producing the cast cold tool.
2. Description of the Prior Art
The aforementioned cold tools are ordinarily made through the steps of forming an ingot by solidifying an molten steel having chemical compositions as a tool steel with C content of not less than 1.0% approximately by weight, subjecting the ingot to hot working by rolling or so and cutting out the hot-worked steel into the predetermined shape.
On the other side, complication in the shape of the cold tool is promoted and there is a movement to introduce near net shaping with a background of improvement in yield rate and reduction of the delivery time at the time of producing the cold tool with the complicated conformation.
As a means for coping with the aforementioned near net shaping, it is considered to start the production from a casting body founded in a shape similar to the desired final shape, and it has been investigated to use the casting body also for the cold tool.
However, in a case of using the cast body with chemical compositions of the conventional cold tool steel, it is not so excellent in toughness and there is a problem in that it is not possible to fit for use in the majority of cases.
It is considered as reasons for the low toughness of the casting body having chemical compositions of the cold tool steel that the cast material lacks of structural uniformity and is apt to be lowered in the toughness, coarse primary carbides are precipitated at the time of founding, therefore nonuniform and coarse cast structure deteriorates the toughness of the cast material, the general purpose cold tool steel is rich in C content, so that the toughness is degraded in a state as it is founded, and so on.